Third-party assessment of contestants during fallow deer fights increases with resource abundance and dominance rank

The decision to engage in escalated fighting involves an interplay between the individual's estimate of the value of the resource under dispute and the ability of the combatants to invest sufficient time and energy in the contest. Although fallow deer, Dama dama, contests usually take place between pairs of individuals, they are sometimes terminated by the intervention of dominant third-party individuals. Theory argues that these interventions prevent subordinates from gaining a competitive boost via a winner effect; thus, interveners benefit by removing this threat to their status. Prior to intervention, third-party individuals often approach and closely follow the competing dyad before either abandoning their interest in the contest, or physically targeting one of the contestants. This study investigated the possibility that third-party following is an assessment process whereby individuals monitor the quality of fighting rivals during the annual rut. We tested three hypotheses: (1) that third-party followers are socially dominant individuals, that (2) follow contests to assess the current quality of high-ranking rivals (3) when resource abundance (i.e. the number of oestrous females) is high. Our results show that socially dominant individuals are most likely to follow contests; however, contrary to expectation, third-party males tended to follow dyads consisting of low-ranking rivals. We also show that as resource abundance increased in the population there was an increased tendency for males to follow contests, and a reduction in the probability of engaging in a third-party intervention of the contest. As expected by theory, dominance and resource abundance were important correlates of third-party following. Our results support the idea that socially dominant males monitor subordinate males that possess sufficient resources to expend in fighting, and that thus may be a threat to their status.